1. Field of the Invention
This invention relates to the testing of electric motors and more specifically to a method and apparatus for testing electric motors for facilitated determination of the operativeness thereof.
2. Description of the Prior Art
During final production testing of an electric motor, visual inspection of rotation of the motor may be impossible or difficult for a variety of reasons. For example, rotation of an output shaft of a timing motor which drives a step-down gear train may be imperceptible over a short time period during which testing should be accomplished. It would be desirable to provide a testing method and apparatus which can determine, in an extremely short time interval, whether an electric motor is operative or inoperative. To maintain a high rate of production, the method must be simple and desirably should require no connection to the output shaft.
It has been known to utilize the residual magnetic field of an electric motor to operate an indicator to indicate that an appliance has completed a cycle. An example of such a device is disclosed in U.S. Pat. No. 3,004,205, issued Oct. 10, 1961, to Barritt and Fuqua, and assigned to the assignee of the present application. In the Barritt et al patent, the end of the cycle of an automatic clothes dryer is signaled by an audible indication which is generated in response to the momentary transient voltage induced in the winding of an electric motor by residual decaying circulating rotor currents existing in the rotating rotor immediately following de-energization of the motor.
The present invention comprises a further improvement in this art over that of the copending application of Donald E. Knoop and Rodney F. Seeland, Ser. No. 524,494, filed Nov. 18, 1974, and owned by the assignee hereof. In said copending application, test apparatus is disclosed and a visual indicator is provided in the test apparatus for indicating the operativeness of the motor being tested. Further, a manually operable control member is provided permitting the operator to effect a test of the motor by automatically bringing the motor to a running condition and de-energizing the motor to determine the existence of the running condition by a suitable indication thereof produced by an EMF generated by the motor as it comes to a stop from the running condition.